MT#8117 add database.(central|pair) configs

Now we have 3 database origins that can be used in CARRIER env:
- database ( slave ro in sync with the db cluster )
- database.central ( rw connection to the db cluster )
- database.pair ( rw local instance )

in PRO env all of them point to the same localhost server.
MT#8117 add database.dbnode constant

We need an id for every mysql ro slave. This needs to be set.